The Story of OpenAL

Open Source and Open Standards: Chapters One through Three. A voyage through one of Loki's free software projects.

At Loki Entertainment Software, we deal
with lots of different kinds of software. From public domain, to
BSD-licensed source, to Free Software under GPL and LGPL, to
proprietary code under contract and NDAs, to closed source hardware
drivers, we encounter it all on a daily basis. Moreover, we also
write a variety of source. The games we port to Linux are not open
source, but our own work is available as free software in projects
like part of projects like Fenris, Setup, SMPEG or SDL.

Crossing the fences from all sides over and over again, and
getting to know both the concerns of free software and open-source
advocates as well as the concerns of publishers and developers, our
priorities have changed. As important as open-source and free
software are, one of our projects in particular developed out of
the recognition that there is something even more important: open,
well-documented standards. That project is OpenAL, and its history
so far is a fair bit of education on how important standards
are—and how difficult it is to create them.

A Case of Need

With the Linux ports of Heretic2 and
Heavy Gear 2, Loki encountered engines that
used spatialized sound above and beyond left-right panning.
Heretic2 for a time served as a showcase for
audio hardware manufacturers: Aureal's A3D and Creative's EAX,
specifically, were both supported. Both competitors at that time
had ventured beyond the DirectSound3D feature set and were
following very different approaches to spatialized sound. Windows
game developers, caught between three different APIs (not counting
the large number of commercial audio SDKs offered for Windows),
more often than not chose to ignore the issue altogether and
refrained from implementing advanced features (unless they decided
to go with one of the SDK offerings that promised to provide a
convenient abstraction). The manufacturers stepped up and in many
cases guided the developer's hand in adding EAX or A3D support to
their engines. Spatialized 3-D sound became a checkbox item, a
feature to be listed on the game box, and for a while the Windows
game developers were offered an easy ride.

Unfortunately, the situation for Linux users was quite
different. Driver support for the SB16 de facto standard had
stabilized, and PCI sound cards, all in all, worked reasonably well
under Linux. Yet, no ALSA or OSS-proprietary or open-source support
for the most advanced features and boards was readily
available.

Developers targeting Apple users found themselves in a
similar situation—while the multimedia APIs on Mac OS might be
more sophisticated and complete than the Linux solutions, they were
even less compatible with DirectSound and equally oblivious to EAX
and A3D features. Windows developers who cared about portability
faced an audio feature set full of shining promises, but without a
portable API. Given the vastly different approaches of the two main
competitors, things were bound to get worse—at a time when
Microsoft didn't even provide DirectSound3D for the NT platform
that many developers preferred.

Creative, a dominant force in the audio hardware market,
found itself challenged by Aureal, a company that attempted to take
its experience with high-end spatialized sound solutions into the
PC consumer market. Aureal proposed “wavetracing”, a proprietary
approach to generating spatialized sound by simulation of sound
propagation and acoustic properties of a scene—essentially, by
submitting scene geometry to the sound driver. It is important to
understand that to a much larger degree than graphics, audio
technology was, and still is, software-based. Both the viable
market for SDKs, like Miles Sound System or QSound's QMixer, and
the evolution of the competing hardware drivers are clear
indications of this. Aureal's advantage was their knowledge of
simulation, the calculation of early reflections and a lot of
optimization work for their drivers. Their disadvantage was the PC
consumer market, an environment in which cheap speakers are added
to budget solutions as an afterthought. Moving high-end audio
processing out of the laboratory and away from the individual
Head-Related Transfer Functions (HRTFs), on a desktop where most
users and most developers didn't really spend much thought on
spatialization, proved to be extraordinarily difficult and, as we
now know, ultimately fatal.

Despite operating at diminishing returns for all their
efforts, Aureal managed to accomplish one thing: to awaken interest
and tentative user demand for better 3-D audio in games. For early
adopters, it became a selling point, and publishers and developers
followed eventually. Creative, which had their own road map to
future audio features, countered by emphasizing their own extended
feature set—a much simpler solution focused on stochastic
reverberation to emulate the effect of late reflections. In a way,
the early and late reflection solutions are complements but the
API's and implementations were fundamentally different, and
Creative had picked well: EAX was easier and simpler to use, and
for all the lack for simulation accuracy, stochastic reverb proved
to be a much more effective audio cue for the noisy, low-end
speaker desktop.

Both companies were considering Linux initiatives. On one
hand, Aureal had a complete software implementation of
“wavetracing”, eventually marketed as “A2D” to support the A3D
feature set on their competitors' sound cards that could have been
the base of a proprietary or even open-source sample
implementation. On the other hand, Aureal's code base was a heavily
optimized assembly, and a Linux port was not a foregone conclusion.
Creative, on the other hand, recruited Linux coders to develop
drivers in-house and looked for ways to support EAX under Linux.
Both APIs were written with respect to Microsoft's DirectX and COM,
but Aureal's geometry-based A3D API had also been inspired by the
OpenGL API. This was one of many examples on the influence of
OpenGL on the development of OpenAL.